Topics of current interest are: 1) control of the expression of human chorionic gonadotropin (hCG), pregnancy-specific Beta-1-glycoprotein (PSBetaG) and alkaline phosphatase in placenta, SV40 tsA-transformed placental, choriocarcinoma, and nontrophoblastic tumor cells; 2) control of the expression of a-fetoprotein (AFP), albumin, and transferrin in liver, SV40 tsA-transformed liver, and hepatoma cells; 3) biosynthesis and processing of AFP, albumin and transferrin in liver cells; 4) biosynthesis and processing of hCG, PSBetaG and alkaline phosphatase in placental cells. In addition to the temperature-sensitive human placental and rat fetal liver cell lines, we have successfully established a temperature-sensitive rat adult hepatocyte line that is dependent on glucocoricoid for differentiation. The adult hepatocyte line should complement the fetal liver line in the study of gene regulation in development, maturation, and carcinogenesis.